doc/plugins/po.mdwn



[[!template id=plugin name=po core=0 author="[[intrigeri]]"]]
[[!tag type/format]]
This plugin adds support for multi-lingual wikis, translated with
gettext, using po4a.
It depends on the Perl Locale::Po4a::Po library (apt-get install po4a).
Introduction
A language is chosen as the "master" one, and any other supported
language is a "slave" one.
A page written in the "master" language is a "master" page. It can be
of any page type supported by ikiwiki, but PO. It does not have to be
named a special way: migration to this plugin does not imply any page
renaming work.
Example: bla/page.mdwn is a "master" Markdown page written in
English; if usedirs is enabled, it is rendered as
bla/page/index.en.html, else as bla/page.en.html.
Any translation of a "master" page into a "slave" language is called
a "slave" page; it is written in the gettext PO format. PO is now
a page type supported by ikiwiki.
Example: bla/page.fr.po is the PO "message catalog" used to
translate bla/page.mdwn into French; if usedirs is enabled, it is
rendered as bla/page/index.fr.html, else as bla/page.fr.html
Configuration
Supported languages
po_master_language is used to set the "master" language in
ikiwiki.setup, such as:
    po_master_language => { 'code' => 'en', 'name' => 'English' }

po_slave_languages is used to set the list of supported "slave"
languages, such as:
    po_slave_languages => { 'fr' => 'Français',
                            'es' => 'Castellano',
                            'de' => 'Deutsch',
    }

Decide which pages are translatable
The po_translatable_pages setting configures what pages are
translatable. It is a [[ikiwiki/PageSpec]], so you have lots of
control over what kind of pages are translatable.
The PO translations files are anyway not considered as being
translatable, so you don't need to worry about excluding them
explicitly from this [[ikiwiki/PageSpec]].
Internal links
The po_link_to option in ikiwiki.setup is used to decide how
internal links should be generated, depending on web server features
and site-specific preferences.
Default linking behavior
If po_link_to is unset, or set to default, ikiwiki's default
linking behavior is preserved: \[[destpage]] links to the master
language's page.
Link to current language
If po_link_to is set to current, \[[destpage]] links to the
destpage's version written in the current page's language, if
available, i.e.:

foo/destpage/index.LL.html if usedirs is enabled
foo/destpage.LL.html if usedirs is disabled

Link to negotiated language
If po_link_to is set to negotiated, \[[page]] links to the
negotiated preferred language, i.e. foo/page/.
(In)compatibility notes:

if usedirs is disabled, it does not make sense to set po_link_to
to negotiated; this option combination is neither implemented
nor allowed.
if the web server does not support Content Negotiation, setting
po_link_to to negotiated will produce a unusable website.

Server support
Apache
Using Apache mod_negotiation makes it really easy to have Apache
serve any page in the client's preferred language, if available.
This is the default Debian Apache configuration.
When usedirs is enabled, one has to set DirectoryIndex index for
the wiki context.
Setting DefaultLanguage LL (replace LL with your default MIME
language code) for the wiki context can help to ensure
bla/page/index.en.html is served as Content-Language: LL.
lighttpd
lighttpd unfortunately does not support content negotiation.
FIXME: does mod_magnet provide the functionality needed to
emulate this?
Usage
Templates
The ISTRANSLATION and ISTRANSLATABLE variables can be used to
display things only on translatable or translation pages.
Display page's versions in other languages
The OTHERLANGUAGES loop provides ways to display other languages'
versions of the same page, and the translations' status.
One typically adds the following code to templates/page.tmpl:
<TMPL_IF NAME="OTHERLANGUAGES">
<div id="otherlanguages">
  <ul>
  <TMPL_LOOP NAME="OTHERLANGUAGES">
    <li>
      <a href="<TMPL_VAR NAME="URL">"><TMPL_VAR NAME="LANGUAGE"></a>
      <TMPL_UNLESS NAME="MASTER">
        (<TMPL_VAR NAME="PERCENT">&nbsp;%)
      </TMPL_UNLESS>
    </li>
  </TMPL_LOOP>
  </ul>
</div>
</TMPL_IF>

The following variables are available inside the loop (for every page in):

URL - url to the page
CODE - two-letters language code
LANGUAGE - language name (as defined in po_slave_languages)
MASTER - is true (1) if, and only if the page is a "master" page
PERCENT - for "slave" pages, is set to the translation completeness, in percents

Display the current translation status
The PERCENTTRANSLATED variable is set to the translation
completeness, expressed in percent, on "slave" pages.
One can use it this way:
<TMPL_IF NAME="ISTRANSLATION">
<div id="percenttranslated">
  <TMPL_VAR NAME="PERCENTTRANSLATED">
</div>
</TMPL_IF>

Additional PageSpec tests
This plugin enhances the regular [[ikiwiki/PageSpec]] syntax with some
additional tests that are documented [[here|ikiwiki/pagespec/po]].
Automatic PO files update
Committing changes to a "master" page:

updates the POT file and the PO files for the supported languages
(this is done in the needsbuild hook); the updated PO files are
then put under version control
triggers a refresh of the corresponding HTML slave pages (this is
achieved by making any "slave" page dependent on the corresponding
"master" page, in the needsbuild hook)

Also, when the plugin has just been enabled, or when a page has just
been declared as being translatable, the needed POT and PO files are
created, and the PO files are checked into version control.
Discussion pages
Discussion should happen in the language in which the pages are written for
real, i.e. the "master" one. If discussion pages are enabled, "slave" pages
therefore link to the "master" page's discussion page.
TODO
OTHERLANGUAGES dependencies
Pages using OTHERLANGUAGES depend on any "master" and "slave" pages
whose status is being displayed. It is supposed to trigger dependency
loops, but no practical bugs were noticed yet.
Should pages using the OTHERLANGUAGES template loop be declared as
linking to the same page in other versions? To be rigorous, they
should, but this may clutter the backlinks.
Security checks

refreshpofiles uses system(), whose args have to be checked more
thoroughly to prevent any security issue (command injection, etc.).
refreshpofiles and refreshpot create new files; this may need
some checks, e.g. using IkiWiki::prep_writefile()

gettext/po4a rough corners

fix infinite loop when synchronizing two ikiwiki (when checkouts
live in different directories): say bla.fr.po has been updated in
repo2; pulling repo2 from repo1 seems to trigger a PO update, that
changes bla.fr.po in repo1; then pushing repo1 to repo2 triggers
a PO update, that changes bla.fr.po in repo2; etc.; fixed in
629968fc89bced6727981c0a1138072631751fee?
new translations created in the web interface must get proper charset/encoding
gettext metadata, else the next automatic PO update removes any non-ascii
chars; possible solution: put such metadata into the Pot file, and let it
propagate; should be fixed in 773de05a7a1ee68d2bed173367cf5e716884945a, time
will tell.

Misc. improvements
automatic POT/PO update
Use the change hook instead of needsbuild?
page titles
Use nice page titles from meta plugin in links, as inline already does.
websetup
Which configuration settings are safe enough for websetup?
parentlinks
When the wiki home page is translatable, the parentlinks plugin sets
./index.html as its translations' single parent link. Ideally, the home page's
translations should get no parent link at all, just like the version written in
the master language.
backlinks
If a given translatable sourcepage.mdwn links to [[destpage]],
sourcepage.LL.po also link to [[destpage]], and the latter has the master
page and all its translations listed in the backlinks.
Translation quality assurance
Modifying a PO file via the CGI must be forbidden if the new version
is not a valid PO file. As a bonus, check that it provides a more
complete translation than the existing one.
A new cansave type of hook would be needed to implement this.
Note: committing to the underlying repository is a way to bypass
this check.
Translating online
As PO is a wiki page type, we already have an online PO editor, that
is ikiwiki's CGI.
FIXME preview does not work for PO files.
A message-by-message interface could also be implemented at some
point; a nice way to do offline translation work (without VCS access)
still has to be offered, though.
Translating offline without VCS access
The following workflow should be made possible for translators without
VCS access who need to edit the PO files in another editor than a web
browser:

download the page's PO file
use any PO editor to update the translation
upload the updated PO file

Implementation note: a generic mechanism to upload a page's source is
needed: it's only an alternative way to allow saving a the modified
page's source with the CGI.
Short-term workflow
A possible workaround is:

pretend to edit the PO file online
copy the PO file content from the textarea
cancel the edit
paste the content into a local file.
edit the local file in any PO editor
pretend to edit the PO file online
paste the modified local file's content into the edit textarea
save